A major source of non-occupational human exposure to 2,2-bis(4-hydroxyphenyl)propane) (a/k/a bis-phenol A, or BPA) is from food can coatings. Interior can coatings, also known as lacquers or enamels, are applied to the interior of cans to prevent corrosion of the can and contamination of food with a metallic taste. As these coatings prevent oxidation of the can, the coatings should have good adhesion to the metal of the can, flow well over the metal surface so that there are no eyeholes or inclusions in the coating, and be durable enough to survive lengthy periods of exposure to often acidic food. The process of coating a can typically involves spraying one or two layers of a coating using an airless spray system (depending on the coating system). This coating is then thermally cured at an elevated temperature, e.g. about 210° C.
While there are several types of can coatings available, many have very limited application due to incompatibilities with food chemistries, or because of their prohibitively high cost. The choice of resin is typically based on cost and the type of product that is inside the can. The vast majority of food and beverage cans produced today are coated with BPA-based phenolic-epoxy resins. However, BPA has been shown to migrate from the coatings on these cans in small amounts into liquids and food products, thereby posing a potential health risk to humans that consume the food. Due to this, coatings with BPA are becoming disfavored, despite their other superior performance properties.
Suggested replacement coatings for BPA in various can applications, include polyethylene terephthalate (PET) resins. However, PET-based coating materials are subject to damage and peel-off during processing of the cans, due to the softness and low adhesiveness.